OFFSET
1,1
COMMENTS
Terms divided by 100, e.g., 29 indicates year 2900, which is a revised Julian leap year, but not a Gregorian leap year. Values below 20 are "proleptic" (only based on the formula).
LINKS
M. Milankovitch, Das Ende des julianischen Kalenders und der neue Kalender der orientalischen Kirchen, Astronomische Nachrichten, volume 220 (1924), 379-384.
Claus Tøndering, Frequently Asked Questions about Calendars, Don't the Greeks do it differently?
Wikipedia, Revised Julian calendar
Index entries for linear recurrences with constant coefficients, signature (1,1,-1).
FORMULA
a(n) = a(n-2) + 9. - Charles R Greathouse IV, Aug 09 2011
a(n) = 2 or 6 (mod 9).
For all positive integers n, a(n) = (1/4)*(18*n-17*(-1)^n-11), which implies a(2*n-1) = 9*n-3 and a(2*n) = 9*n-7. - Farideh Firoozbakht, Oct 08 2014
G.f.: x*(2 + 4*x + 3*x^2)/((1 + x)*(1 - x)^2). - Philippe Deléham, Nov 30 2016
EXAMPLE
MATHEMATICA
Table[1/4 (18 m - (-1)^m - 11), {m, 56}] (* Farideh Firoozbakht, Oct 08 2014 *)
PROG
(Rexx) do C = 0 to 250; J = C // 9; if J = 2 | J = 6 then say C; end C
(PARI) a(n)=(9*n-5)\2 \\ Charles R Greathouse IV, Aug 23 2011
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Frank Ellermann, Aug 09 2011
STATUS
approved